Saturday, December 17, 2011

Another First of the New Season: The Mayfly Family Ameletidae

This morning, I made a quick trip to one of the Moormans tributaries that I explore, and as always, I was pleased to see the variety of insects that inhabit these streams.  Peltoperlids (Roach-like stoneflies), Pteronarcyds (Giant stoneflies), Chloroperlids (Green stoneflies), Capniids (Small winter stoneflies), Crane fly larvae (two genera: Tipula and Hexatoma), Clioperla Perlodid stoneflies, and more.  And I'll focus on the more.

I only found two mayflies today.  One was a flathead (Maccaffertium, species TBD), but the other was this  Ameletid (genus Ameletus), a mayfly nymph that we only find in small, clean, cold streams.  (The stream that I went to this morning was about 6-9' wide.)  This is a young one, and we'll be watching these nymphs develop over the winter and into the spring.  (Note how the gills stick out to the sides vertically, not horizontally as we see with their brushlegged cousins.)

And, I found a number of Large winter stoneflies -- again Taenionema atlanticum.  I found only three of these nymphs last spring, and now I'm running into them all over the place (well, in very good, very small streams.)  This is a species of Large winter stonefly that I never saw when I officially monitored streams.  But then we never examined streams this tiny in size and, in general, none of the streams that we looked at were ever this good.

And now for the shot of the day -- look at this photo I got of a black fly larva!

I'm not sure I'll ever do any better for a live photo.  Note that you can see the "prolegs" very well, and one of the things that indicates the genus on this one -- Prosimulium -- can also be detected: the dark tip of the antenna.  (Click on the photo to enlarge it.)

Pretty amazing.  Black flies are showing up now: I've seen them in more than one stream.  And, this is the genus we normally see in the winter.  Prosimulium black flies tend to be less tolerant than the Simulium black flies we see in the spring, summer, and fall.  In the NCDWQ list of tolerance values, for species were the values are known, Prosimulium larvae values are 3.6 and 4.5, those for Simulium larvae are 4.9, 7.3, and 9.1.

Peckarsky,, Freshwater Macroinvertebrates, pp. 204-207, note the defining features of Prosimulium in the following way:

"Postocciput nearly complete dorsally and enclosing cervical sclerites; basal 2 segments of antennae pale, strongly contrasting with darkly pigmented distal segments."  In microscope photos, those features are readily seen.

No comments:

Post a Comment